The synthesis of preferred polybenzimidazole-based, high-performance fibers typically involves the selective condensation polymerization of 1,2,4,5-tetraminobenzene (“TAB”) with various substituted and unsubstituted aromatic diacids or derivatives thereof.
Previously known polymers TAB-based polymers were synthesized, for example, from TAB.4HCl and acid chlorides, but they had a molecular weight or intrinsic viscosity that was too low to produce fibers with desirably high mechanical properties such as high tensile strength fiber.
When TAB is polymerized with a monomer such as 2,5-dihydroxyterephthalic acid (“DHTA”), it is desired that the ratio of tetraamine to diacid be as close to 1:1 as possible to achieve a high molecular weight polymer of fiber-grade purity. Production of high molecular weight polymer typically requires a high space time yield process wherein a 1:1 complex between diacid and tetraamine is polymerized. In such a process, there are also safety concerns, especially with respect to sensitizing properties of some intermediates, that need to be addressed
There thus remains a need for a process for the production of a suitable TAB-diacid monomer complex that can be polymerized to a high molecular weight polymer material for producing high-performance fibers, wherein the complex is formed from a stable precursor without isolation of intermediates.